Intelligence tip-off grounds British Airways flight

Security concerns prompted the cancellation of the same British Airways flight from London that US authorities had boarded the night before when it landed at Washington Dulles International Airport.

US officials were acting on intelligence information - and not just suspicious passenger names - when they boarded a British Airways jet on New Year's Eve at Dulles, a national security official said.

The flight cancelled today was one of the airline's three daily flights from Heathrow Airport to Washington. The decision was based on security advice from the British government, a spokesman for British Airways said.

In the New Year's Eve incident, investigators found no evidence of terrorism, and the major consequence appeared to be inconvenience, with the 247 passengers from London waiting more than 3-1/2 hours before getting off the plane while some of them were questioned.

"We had concerns with individuals on the flight, but threat-reporting information led us to make the decision to have the flight escorted," a national security official said, speaking only on condition of anonymity.

"It was fact-related," the official said, and not just connected to the passenger list the United States now receives from airlines flying into this country.

The US official said the long delay was caused in part by weapons screening of passengers, and partly because authorities waited for some law enforcement specialists to arrive.

Transportation Security Administration spokeswoman Jennifer Marty said officials began departing from the plane about 10.30pm, long after the 7.06pm landing.

The plane was kept several hundred metres from the terminal during the questioning.

Passenger David Litwick told WJLA-TV in Washington that he and his wife were not questioned, but at least one other passenger was. Litwick said four FBI agents spoke to a woman who appeared to be from the Middle East, repeatedly asking her why she was not travelling with her husband.

Earlier this week, a scheduled US-bound flight from Mexico was cancelled because of security concerns.

"The government of Mexico made the decision to cancel Aeromexico Flight 490 after the US government shared threat information with the Mexican government," Department of Homeland Security spokesman Brian Roehrkasse said.

Previous reports said the plane turned around in midair, but Roehrkasse and Mexican officials said it never took off. Roehrkasse denied that the US government told Mexico it would refuse the plane landing rights.

However, Agustin Gutierrez, Mexico's presidential spokesman, said the flight was cancelled after United States authorities said they would refuse to allow it to land.

He also said Mexico did not receive convincing information for the cancellation.

"The question is what threat?" Gutierrez said. "This question must be answered by Homeland Security. If we are going to have a good climate of cooperation, the least that we can hope for are reasons."

The threat of terrorism also prompted the closure on Tuesday night of the oil tanker terminal in Valdez, Alaska. The terminal remained closed today, Lt Cmdr Jeff Carter of the Coast Guard said.

Tankers load Prudhoe Bay oil destined for the Lower 48 states at Valdez, the end of the 1,280km pipeline, which carries 17 per cent of the nation's domestic oil supply.

Last week, security was strengthened in the Prince William Sound community after US officials said al-Qaeda operatives could target remote sites such as oil facilities in Alaska.

Officials also said then they could not corroborate a report about an al-Qaeda threat against the Valdez oil terminal.